U.S. patent number 9,190,718 [Application Number 13/103,084] was granted by the patent office on 2015-11-17 for efficient front end and antenna implementation.
This patent grant is currently assigned to MAXTENA. The grantee listed for this patent is Carlo DiNallo, Stani Licul, Jeremy Marks. Invention is credited to Carlo DiNallo, Stani Licul, Jeremy Marks.
United States Patent |
9,190,718 |
DiNallo , et al. |
November 17, 2015 |
Efficient front end and antenna implementation
Abstract
A tightly integrated combined transmit and receive dual
quadrifilar antenna is provided. The antenna comprises four helical
transmit elements and four helical receive elements disposed about
a common axis. A receiver front end includes an arrangement of two
90 degree hybrids which serve to effectively reject signals cross
coupled from the transmit elements back into the receive elements,
while still allowing the receiver to receive signals.
Inventors: |
DiNallo; Carlo (Plantation,
FL), Licul; Stani (North Bethesda, MD), Marks; Jeremy
(Atlanta, GA) |
Applicant: |
Name |
City |
State |
Country |
Type |
DiNallo; Carlo
Licul; Stani
Marks; Jeremy |
Plantation
North Bethesda
Atlanta |
FL
MD
GA |
US
US
US |
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|
Assignee: |
MAXTENA (Rockville,
MD)
|
Family
ID: |
47627227 |
Appl.
No.: |
13/103,084 |
Filed: |
May 8, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130035044 A1 |
Feb 7, 2013 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61332761 |
May 8, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01Q
11/08 (20130101); H01Q 1/36 (20130101) |
Current International
Class: |
H01Q
1/36 (20060101); H01Q 11/08 (20060101); H04B
1/38 (20150101); H04M 1/00 (20060101) |
Field of
Search: |
;455/73,562.1,575.7
;343/895 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ayotunde; Ayodeji
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Parent Case Text
RELATED APPLICATION DATA
This application claims the benefit of U.S. provisional application
No. 61/332,761 filed May 8, 2010.
Claims
We claim:
1. An antenna assembly comprising: a set of four transmit antenna
elements including a first transmit antenna element, a second
transmit antenna element, a third transmit antenna element and a
fourth transmit antenna element, wherein said set of four transmit
elements are arranged in order about an axis and are equally spaced
about said axis in azimuth angle; a set of four receive antenna
elements including a first receive antenna element, a second
receive antenna element disposed adjacent said first receive
element, a third receive antenna element disposed adjacent said
second receive antenna element and a fourth receive antenna element
disposed adjacent said third receive antenna element and said first
receive antenna element, wherein said set of four receive antenna
elements are arranged in order about said axis, equally spaced
about said axis in azimuth angle; a transmitter front end coupled
to said set of four transmit elements; a receiver front end coupled
to said set of four receive elements.
2. The antenna assembly according to claim 1 wherein said
transmitter front end is adapted to provide four signals to said
set of four transmit antenna elements wherein, in proceeding from
transmit antenna element to transmit antenna element azimuthally in
a predetermined azimuth direction, each successive element receives
a signal that has a phase that is advanced by 90 degrees relative
to a signal applied to a preceding element.
3. The antenna assembly according to claim 2 wherein: said receiver
front end comprises a first 90 degree hybrid coupled to said first
receive element and said second receive element and a second 90
degree hybrid coupled to said third receive element and said fourth
receive element.
4. The antenna assembly according to claim 3 wherein said
transmitter front end comprises a third 90 degree hybrid coupled to
said first transmit element and said second transmit element and a
fourth 90 degree hybrid coupled to said third transmit element and
said fourth transmit element.
5. The antenna assembly according to claim 3 wherein: said receiver
front end further comprises a balun coupled to said first 90 degree
hybrid and said second 90 degree hybrid.
6. The antenna assembly according to claim 5 further comprising: a
first low noise amplifier coupled between said first 90 degree
hybrid and said balun; a second low noise amplifier coupled between
said second 90 degree hybrid and said balun.
7. The antenna assembly according to claim 3 wherein: said receiver
front end further comprises a differential input low noise
amplifier coupled to said first 90 degree hybrid and said second 90
degree hybrid.
8. The antenna assembly according to claim 2 wherein said
transmitter front end comprises a first 90 degree hybrid coupled to
said first transmit element and said second transmit element and a
second 90 degree hybrid coupled to said third transmit element and
said fourth transmit element.
9. The antenna assembly according to claim 8 wherein: said
transmitter front end further comprises a balun coupled to said
first 90 degree hybrid and said second 90 degree hybrid.
10. The antenna assembly according to claim 9 further comprising: a
first power amplifier coupled between said balun and said first 90
degree hybrid; a second power amplifier coupled between said balun
and said second 90 degree hybrid.
11. The antenna assembly according to claim 9 wherein: said
transmitter front end further comprises a differential output power
amplifier coupled to said first 90 degree hybrid and said second 90
degree hybrid.
12. The antenna assembly according to claim 1 wherein each of said
receive elements is equally spaced from two of said transmit
elements.
13. The antenna assembly to claim 1 wherein said receive antenna
elements and said transmit antenna elements are disposed on a
common surface.
14. The antenna assembly according to claim 13 wherein said common
surface is a cylindrical surface.
15. The antenna assembly according to claim 13 wherein said common
surface is hemispherical.
16. The antenna assembly according to claim 13 wherein said common
surface is frusto conical.
17. The antenna assembly according to claim 1 where said receive
antenna elements are disposed on a first surface and said transmit
antenna elements are disposed on a second surface that is coaxial
with said first surface.
18. The antenna assembly according to claim 17 wherein said first
surface is cylindrical and said second surface is cylindrical.
19. The antenna assembly according to claim 1 wherein said receive
antenna elements and said transmit antenna elements are
helical.
20. The antenna assembly according to claim 1 wherein a gain
pattern of said set of four receive elements is substantially equal
to a gain pattern of said set of four transmit elements.
21. The antenna assembly according to claim 1 wherein said receive
elements are tuned to a first frequency and said transmit elements
are tuned to a second frequency.
Description
FIELD OF THE INVENTION
The present invention relates to the field of antennas and
transceiver architecture for satellite and mobile
communications.
DESCRIPTION OF RELATED ART
In every two-way communication device the transmit (Tx) and receive
(Rx) operations have to be properly isolated to avoid self
interference. This separation, termed duplexing, is accomplished in
many different ways such as for example by allocating different
time slots for receiving and transmitting or by using two different
frequency bands. In most wireless systems the duplexing function is
performed by the transceiver front end and the Tx and Rx ports are
combined and connected to a single antenna. This is by far the most
commonly used architecture.
Alternatively, two separate antennas can be used, but this solution
requires additional volume and does not necessarily provide the
minimum required isolation. Isolation between Tx and Rx antennas
can be obtained by designing antenna structures exciting orthogonal
electromagnetic fields. However, building orthogonal antennas
usually proves to be difficult and it is rarely done in practical
systems. Moreover, orthogonal structures generate orthogonal
polarizations and radiation patterns. This is not acceptable in
many cases as the Tx and Rx antennas are required to have similar
polarization and pattern characteristics. In satellite
communications, for instance, the antennas need to have similar
gain in the same direction.
A fractional-turn Quadrifilar Helix Antenna (QHA) disclosed in US
Patent Application Publication 2008/0174501 A1 assigned in common
with the present invention. Its pattern is nearly hemispherical and
can be shaped to favor a particular elevation angle, if needed.
Circular polarization is almost ideal over a very wide range of
elevation angle. The most compact variant of the QHA has four
helical elements with electrical length of about 1/4 wavelength fed
by a 4-port phase shifting network enforcing the proper phase
rotation. A QHA is shown in FIG. 13. A detailed description of the
possible implementation of the feeding network can be found in US
2008/0174501.
What is needed is an antenna system that is capable of
simultaneously transmitting and receiving without having the
transmitted signal overwhelm received signals and that exhibits
substantially equal radiation patterns for both transmitting and
receiving.
DESCRIPTION OF THE FIGURES
The present invention will be described by way of exemplary
embodiments, but not limitations, illustrated in the accompanying
drawings in which like references denote similar elements, and in
which:
FIG. 1 is a schematic illustration of an antenna according to a
first embodiment of the invention;
FIGS. 2A, 2B, 2C illustrate an antenna according to a second
embodiment of the invention;
FIG. 3 is a plot showing the radiation patterns (in a vertical
plane) for the antenna shown in FIG. 1;
FIG. 4 is a schematic illustration of a feed network that is used
to feed quadrifilar antennas according to certain embodiments of
the invention;
FIG. 5 describes the operation of a 90 degree hybrid when fed with
a signal at a common input port;
FIG. 6 describes the operation of a 90 degree hybrid when 2 signals
of equal amplitude and in phase quadrature are fed to the 2 output
ports;
FIG. 7 describes the spatial relationship between receiving and
transmitting elements in one embodiment of the invention and
illustrates the effect of the geometrical symmetry of the
arrangement shown on the intercoupling between the elements;
FIG. 8 illustrates a phase cancellation effect that is achieved in
embodiments of the invention, and that provides for very good
isolation between the transmitted and received signals;
FIG. 9 is a schematic illustration of a transceiver front end, used
in combination with the antennas shown in FIG. 1 and FIG. 2 and
variations thereof according to embodiments of the invention;
FIG. 10 is an schematic illustration of a transceiver front end,
that uses differential amplifiers and that can be used in
combination with the antennas shown in FIG. 1 and FIG. 2 and
variations thereof according to embodiments of the invention;
FIG. 11 is a schematic illustration of an antenna that includes
four helical transmit elements and four helical receive elements
arranged on a conical surface according to an embodiment of the
invention; and
FIG. 12 is a schematic illustration of an antenna that includes
four helical receive elements and four helical transmit elements
conforming to a hemispherical surface according to an embodiment of
the invention; and
FIG. 13 shows a single quadrifilar antenna and indicates the
phasing of a 4 port feeding network for the antenna.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As required, detailed embodiments of the present invention are
disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention, which
can be embodied in various forms. Therefore, specific structural
and functional details disclosed herein are not to be interpreted
as limiting, but merely as a basis for the claims and as a
representative basis for teaching one skilled in the art to
variously employ the present invention in virtually any
appropriately detailed structure. Further, the terms and phrases
used herein are not intended to be limiting; but rather, to provide
an understandable description of the invention.
The present invention provides an integrated dual Transmit/Receive
quadrifilar antenna, applicable to any communication system using
separate transmit and receive frequency bands. A system that uses
the antenna to achieve transceiver duplexing is also disclosed. The
antennas exhibit a substantially equal radiation patterns for
transmitting and receiving functions. Isolation between
transmission and reception channels connected to the antenna is
achieved through phase cancellation in the antennas feeding
network. A differential transceiver architecture that is
particularly convenient when used in combination with the antenna
is also disclosed.
The basic embodiment of the invention encompasses two quadrifilar
helices having the same or different diameter. Each of the
quadrifilar helices comprises four helical antenna elements. The
two quadrifilar helices are tuned to different frequencies,
corresponding to the centers of the Tx and Rx bands respectively
and are spatially rotated 45 degrees with respect to each
other.
According to the present invention antennas are provided that
include two co-located quadrifilar helices. The two quadrifilar
helices are used to perform the Tx and Rx duplexing function of the
transceiver. For reference a cylindrical quadrifilar antenna is
shown in FIG. 13, with the relevant phase impressed at each element
by the feeding network. While a cylindrical shape is shown, the
present invention applies to quadrifilar structures of any shape,
such as conical or spherical.
According to embodiments of the invention the two quadrifilar
helices are tuned at different frequencies corresponding to the Tx
and Rx band of the communication system. The two quadrafilar
helices share the same axis of symmetry (e.g., axis `w` in FIG. 1)
and can have the same radius or be placed one inside the other
one.
FIG. 1 is a schematic illustration of an antenna 100 according to a
first embodiment of the invention. The antenna 100 includes two
quadrifilar helices located about a common axis, `w` on a common
surface. A first quadrifilar helix is made up of four helical
transmit elements 102. A second quadrifilar helix is made up of
four helical receive elements 104. The four receive elements 104
are shorter than the four transmit helical elements 102 and are
thus tuned to a higher frequency of operation. Alternatively the
frequency relationships of the transmit and receive elements may be
reversed. The four receive elements 104 are equally spaced in
azimuth angle about the axis `w`. The four transmit elements 102
are also equally spaced in azimuth angle about the axis `w`. The
helical transmit elements 102 and the helical receive elements 104
alternate in position when proceeding azimuthally about the axis of
symmetry, `w` of the antenna 100. Each receive element 102 is
preferably equally spaced from its two neighboring transmit
elements 104 and vis-a-versa.
The surface on which the elements 102, 104 are disposed may be a
virtual (e.g., mathematically defined) surface in the case that the
helices are self-supporting. Alternatively the surface is the real
surface of a dielectric (e.g., plastic, ceramic) support that
supports the helices. In FIG. 1 no real surface is shown-the
surface is virtual. The surface may for example be cylindrical,
hemispherical, or frusto conical. A ground reference structure 106
for the antenna 100 takes the form of a ground plane of a printed
circuit board 108 on which the antenna 100 is supported.
FIGS. 2A, 2B, 2C illustrate an antenna 200 according to a second
embodiment of the invention. The antenna 200 includes an inner
quadrifilar helix 202 nested within an outer quadrifilar helix 204.
The inner and outer quadrifilar helices 202, 204 are coaxial,
sharing a common axis `w`. The inner quadrifilar helix 202
comprises four helical transmit elements 206 and the outer
quadrifilar helix 204 comprises four helical receive elements 208.
The four helical transmit elements 206 are disposed on an inner
cylindrical surface 209 and the four helical receive elements 208
are disposed on an outer cylindrical surface 210 that is coaxial
with the inner cylindrical surface 209 sharing the common axis
`w`.
In the antenna 200 the helical elements 206, 208 can have the same
or different height because the difference in diameter between the
inner and outer quadrifilar helices 202, 204 introduces a
difference in the frequency tuning. However, it is convenient to
make the inner quadrifilar helix 202 operate in a higher frequency
band, and make the outer quadrifilar helix 204, with its larger
diameter, operate in a lower frequency band.
FIG. 3 is a graph of the radiation pattern in a vertical plane for
an embodiment of the type shown in FIG. 1. The curve 302 is the
gain (in a plane containing the axis of symmetry, `w` of the
antenna) for the lower band antenna and while curve 304 represents
the gain for the higher band antenna. The radiation characteristics
are very similar and both are circularly polarized.
In quadrifilar antenna systems the helical antenna elements are fed
through a 4-port phase shifting network enforcing the proper phase
rotation. Usually the phase rotation is the same for both the Tx
and Rx antennas. According to embodiments of the invention 90
degrees hybrid couplers are used to enforce the phase shifting.
FIG. 4 is a schematic illustration of a feed network 400 that is
used in combination with dual quadrifilar antennas described above
with reference to FIG. 1 and FIG. 2 according to embodiments of the
invention. The same feed network 400 is useful for both the receive
quadrifilar helices and the transmit quadrifilar helices, although
in each case a different arrangement of amplifiers is used.
Referring to the FIG. 4 an unbalanced terminal 401 of a balun 412
serves as a connection to other receiver or transmitter circuits
(not shown) such as for example modulators or demodulators. The
balun 412 also comprises a ground terminal coupled to a system
ground 410 with respect to which the unbalanced terminal 401 is
driven. The balun 412 further comprises a 0.degree. balanced-side
port 413 and a 180.degree. balanced-side port 415. The 0.degree.
balanced-side port 413 is coupled to an input port 417 of a first
90.degree. hybrid 403 and the 180.degree. balanced-side port 415 is
coupled to an input port 419 of a second 90.degree. hybrid 405. The
90.degree. hybrids 403, 405 also comprise ground terminals coupled
to the system ground 410. The first 90.degree. hybrid 403 includes
a second port 402 phased at 0.degree. and a third port 404 phased
at 90.degree.. The second 90.degree. hybrid includes a second port
406 and a third port 408. Because the input port 419 of the second
90.degree. hybrid 405 is coupled to the 180.degree. balanced-side
port 415 of the balun 412, the second port 406 is phased at
180.degree. and the third port 408 is phased at 270.degree.. Thus
considering the second ports 402, 406 and third ports 404, 408 of
the 90.degree. hybrids 403, 405 it is seen that four phases of the
signal appearing at unbalanced terminal 401 will be present at the
these ports 402, 406, 404, 408. The signals appearing at ports 402,
404, 406, 408 are spaced apart by 90.degree.. The ports 402, 404,
406, 408 with respective phases 0.degree., 90.degree., 180.degree.,
270.degree., will be coupled to four elements of a quadrifilar
helix such that phase increases in uniform steps of 90.degree. when
proceeding in a predetermined azimuth direction (i.e., CW or CCW)
from one helical antenna element to a succeeding helical antenna
element. FIGS. 5 and 6 illustrates the operation of a 90.degree.
hybrid 500 which is equivalent to the 90.degree. hybrids 403, 405
shown in FIG. 4. The 90.degree. hybrid 500 has two quadrature ports
501, 502 for coupling to antenna elements, one input port 503 and
one isolated port 504 which is terminated with an resistive load
505 which is usually a 50 Ohm load. When a signal is fed to the
input port 503, as illustrated in FIG. 5, the signal is split
equally between the 2 quadrature ports 501, 502, with, for
instance, +90.degree. phase difference between them. No signal is
coupled in theory to the isolated port 504. However, if two signals
of equal amplitude are applied to the quadrature ports 501, 502
with the same relative phase difference of 90 degrees, as
exemplified in FIG. 6, all the power is transferred to the isolated
port 504 and absorbed by the resistive load 505.
The feed network 400 is suitably implemented on a Printed Circuit
Board (PCB) that also includes the ground reference structure
(e.g., ground plane) for the antennas. A simple and effective
implementation of the design is obtained by placing Tx and Rx phase
shifting networks on the top and bottom layer of the PCB
respectively. The ground plane is suitably embodied in a middle
layer placed between the top and bottom layers of the PCB.
In general the out of band rejection of an antenna is not enough to
provide the required Tx/Rx isolation. In practical communication
systems the Tx and Rx bands are relatively close to each other in
frequency. The frequency separation only provides 10 to 15 dB
isolation between the Tx and Rx antenna. Such isolation is too poor
for the system to work properly. A more realistic isolation value
in practical system is 40-50 dB.
FIG. 7 illustrates how additional isolation is obtained by using
the embodiments of the invention. Transmit elements are represented
by black dots and receive elements are represented by unfilled
circles. Because of the rotational symmetry of the structure it can
be recognized that each transmitting element is at an equal shorter
distance D1 from two of the receiving elements and at an equal
larger distance D2 from the other two receiving elements. It can be
demonstrated that the amount of power coupled by a single
transmitting element into each receiving element is the same if the
distance is the same as depicted in FIG. 7, where a indicates the
signal coupled to the closer elements and b the signal coupled to
the farther elements. Since each transmitting element is fed with
the same amplitude s and known phase, it is possible to calculate
the summed signal coupled by all the transmitting elements to each
individual receiving element.
FIG. 8 is a schematic plan view of an antenna system 800
highlighting the manner in which signals cross coupled from a set
of transmit antenna elements 810, 812, 814, 816 into a set of
receive antenna elements 818, 820, 822, 824 are effectively
rejected by a receiver front end. The antenna system 800 includes
(proceeding in clockwise order from the upper left) a first
transmit antenna element 810, a first receive antenna element 818,
a second transmit antenna element 812, a second receive antenna
element 820, a third transmit antenna element 814, a third receive
antenna element 822 a fourth transmit antenna element 816 and a
fourth receive antenna element 824. The aforementioned antenna
elements are equally spaced in azimuth angle. Mathematical
expressions adjacent to each particular receive antenna element
give the sum of signals cross-coupled to the particular receive
antenna element from the transmit antenna elements. Signals coupled
from the transmit antenna elements to the receive antenna elements
are combined into the 90 degrees hybrid couplers 802 and 804 as
indicated in FIG. 8. The result is a complete cancellation of the
signal coupled from the transmit antenna element to into the
receive antenna elements at the hybrids input ports 503 (FIG. 5, 6)
and an in phase combination of the coupled signals at the isolated
port 504 (FIG. 5, 6). Since the isolated ports 504 are connected to
a 50 ohm loads 806, 808, the signal coupled from the transmit
antenna elements to the receive antenna elements is suppressed and
does not affect the receiver chain (e.g., demodulator, decoder, not
shown).
FIG. 9 is a schematic illustration of a transceiver front end 900,
used in combination with the antennas shown in FIG. 1 and FIG. 2
and variations thereof according to embodiments of the invention.
The transceiver front end 900 comprises a transmitter front end 902
and a receiver front end 904. The architecture of both of the
transmitter front end 902 and receiver front end 904 conform to the
schematic shown in FIG. 4 excepting the addition of a pair of Low
Noise Amplifiers (LNA) 906, 908 in the receiver front end 904 and a
pair of Power Amplifiers (PA) 910, 912 in the transmitter front end
902.
In the receiver front end 904, two inputs 907 of the two LNAs 906,
908 are connected to the `input` (serving here as outputs) ports
417, 419 of the receiver 90.degree. hydrids 403, 405, forming the
feeding network of a receiving antenna (e.g., 100, 200). Two
outputs 909 of the two LNAs 906, 908 are coupled to 0.degree. and
180.degree. balanced side ports 413, 415 of the balun 412. The LNAs
906, 908 are driven by signals in phase opposition and the total
received signal can be combined after amplification through the use
of the balun 412. Alternatively a single differential LNA can be
used in lieu of the two LNAs 906, 908.
In the transmitter front end 902 a first PA 910 is interposed
between the 0.degree. balanced-side port 413 of the balun 412 and
the input port 417 of a first 90.degree. hybrid 403; and a second
PA 912 is interposed between the 180.degree. balanced-side port 415
of the balun 412 and the input port 419 of a second 90.degree.
hybrid 405. Differential phasing is obtained by using the balun 412
to split the Tx signal. Alternatively a single differential PA can
be used. According to certain embodiments the functions of the
balun 412 may be embodied in a frequency filter component
FIG. 10 is a schematic illustration of a transceiver front end 1000
that uses differential amplifiers 1002, 1004 in lieu of the
amplifiers 906,908, 910, 912 used in the embodiment shown in FIG.
9. The function of the balun in this embodiment is integrated in
the differential amplifiers 1002, 1004 and baluns 412 are no longer
needed. A differential input low noise amplifier 1002 includes a
pair of inputs 1006 that are coupled to the inputs (here serving as
an output) 417, 419 of the first and second 90.degree. hybrids of a
receiver part 1008 of the transceiver front end 1000. An output
1010 of the differential input low noise amplifier 1002 serves as
an output of the receiver 1008.
In a transmitter part 1012 of the transceiver front end 1000 a
differential output PA 1004 includes a pair of differential outputs
1014 that are coupled to inputs 417, 419 of the first and second
90.degree. hybrids of the transmitter part 1012. An input 1016 of
the differential output PA 1004 serves as an input of the
transmitter part 1012.
FIG. 11 shows an antenna 1100 according to an embodiment of the
present invention. The antenna 1100 includes four transmit elements
1102 and four receive elements 1104 arranged on a frusto conical
surface 1106.
FIG. 12 shows an antenna 1200 according to an embodiment of the
present invention. The antenna 1200 includes four transmit elements
1202 and four receive elements 1204 conforming to a hemispherical
surface 1206.
The antenna systems described above provide advantages in terms of
filtering, linearity, power handling capacity and noise
suppression. Moreover the cancellation of signals cross coupled
from the transmit elements to the receive elements that is obtained
in such antenna systems provides an additional 3 dB to Tx/Rx
isolation. The antenna systems described above can be use singly or
in a phased array arrangement.
While particular embodiments of the invention has been described
above with reference to the accompanying figures, various
variations and modification of the invention are possible and will
apparent to those of ordinary skill in the art, and the invention
should not be construed as limited to the particular embodiments
shown and described and should only be construed as limited by the
appended claims.
* * * * *